Method and apparatus for manufacturing a semiconductor device

ABSTRACT

In forming various types of insulating films in manufacture of a semiconductor device, carbon is gasified into CH x , COH etc. during film formation by adding active hydrogen and nitrogen oxide to reduce the carbon content during the film formation, and the effect of blocking impurities such as alkali metals is improved.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to film formation using an organicsilane type source gas. More specifically, the invention relates to amanufacturing method of a semiconductor device including formation of afilm containing hydrogen and nitrogen which film is low in the contentof carbon components and superior both in step coverage and impurityblocking performance.

[0003] 2. Description of the Related Art

[0004] In LSIs, which constitute one technical field of semiconductordevices, the wiring interval is now as small as 0.2-0.4 μm and theaspect ratio (height to width) of wiring lines (interconnections) nowexceeds unity. To prevent voids from occurring in planarizing aninterlayer insulating film, a film forming method comes to be used whichutilizes superior step coverage of a film that is formed by using anorganic silane type source gas such as ethyl orthosilicate (Si(OC₂H₅)₄,what is called “TEOS”). In another field of liquid crystal displays inwhich a number of thin-film transistors are formed on an insulativesubstrate, the frequency of occurrence of what is called a “break at astep” of wiring lines of thin-film transistors is lowered by utilizingsuperior step coverage of a film formed by using ethyl orthosilicate asa source gas. In particular, in liquid crystal displays using a processof lower than 600° C. in contrast to high-temperature processes forsilicon wafers, an ethyl orthosilicate source gas is used to form a gateoxide film and an undercoat film in addition to an interlayer insulatingfilm.

[0005] In the field of LSIs, although an oxide film formed by usingethyl orthosilicate is used as an interlayer insulating film, itcontains many carbon-hydrogen bonds and oxygen-hydrogen bonds andtherefore is high in hygroscopicity. On the other hand, although asilicon nitride film exhibits high water resistance and impurityblocking performance, it is inferior in step coverage and is easilybroken because of its high degree of hardness.

[0006] In thin-film transistors (TFTs), which are applied to, forinstance, a liquid crystal display, an undercoat film, a gate insulatingfilm, an interlayer insulating film, and the like are formed on aninsulative substrate such as a glass substrate by thermal CVD, plasmaCVD, or a like method by -using an organic silane type source gas suchas ethyl orthosilicate. However, having a large amount of carbon, suchfilms are not sufficient in terms of water resistance and impurityblocking performance.

[0007] In a conventional, commonly employed film forming method that isa plasma CVD method using ethyl orthosilicate, a subject substrate isplaced in a chamber having parallel-plate electrodes and capable ofbeing evacuated. On of the electrodes is connected to a high-frequencypower supply, that is, serves as the cathode. The other electrode isconnected to the ground, that is, serves as the anode. The subjectsubstrate is placed on the ground-side, i.e., anode-side electrode.Since ethyl orthosilicate assumes liquid form in the ordinarytemperature, it is introduced into the chamber in a state that it isheated to increase its vapor pressure or it is introduced into thechamber together with a carrier gas by bubbling ethyl orthosilicate in atank with the carrier gas. Ethyl orthosilicate has a feature that whendecomposed in plasma, it forms precursors and flows on the substrate,thus enabling formation of a film that is superior is step coverage.Precursors moving on the substrate collide with each other, and oxygenions, oxygen radicals, ozone molecules formed in the plasma collide withthose precursors, causing abstraction reaction on the surface andthereby forming SiO_(x). If a larger amount of oxygen is introduced, thesurface abstraction reaction due to the precursors that are formed fromethyl orthosilicate is accelerated. In this case, the step coverage isdegraded though the carbon content is reduced.

[0008] On the other hand, if a smaller amount of oxygen is introduced,although the step coverage is improved, more carbon-hydrogen andoxygen-hydrogen bonds remain in the film, making it highly hygroscopic.If an infrared measurement is conducted, the absorption in the vicinityof 3,660 cm⁻¹ will increase with the lapse of time. The absorption at3,660 cm⁻¹ is mainly due to Si—OH bonds and indicates that a film formedis hygroscopic.

[0009] Another film forming method using ethyl orthosilicate is anatmospheric pressure CVD method utilizing ozone and heat. In thismethod, a substrate is heated to 300-400° C. An organic silane typesource gas such as ethyl orthosilicate is introduced into a reactionchamber by bubbling it in a tank with N₂. Ozone is also introduced intothe chamber by generating it by passing oxygen through an ozonizer.Because of superior step coverage and a high film forming rate of thismethod, this method is used to form an interlayer insulating film fordevices that include multi-layer wiring, such as LSIs and DRAMsmemories. After the film formation, planarization is performed byetching back, SOG (spin on glass), CMP (chemical mechanical polishing),etc. in combination.

[0010] However, according to the above atmospheric pressure CVD method,a resulting film is very low in density, that is, a porous film isformed. Therefore, if such a film is used singly, it exhibits very highhygroscopicity, possibly causing leak between wiring lines, thuslowering the reliability of a semiconductor device. Further, at thepresent time when the application of the 0.3-μm rules is pressing, thelateral capacitance between wiring lines is not negligible, whichrequires a film having a small permittivity.

[0011] Japanese Unexamined Patent Publication No. Hei. 1-48425 of thepresent assignee discloses a film forming method that uses an organicsilane type source gas and nitrogen oxide. As disclosed in the abovepublication, this method can form a uniform coating on an uneven surfacewhich coating blocks alkaline impurities. Although this coatingfunctions satisfactorily when used only as an interlayer insulatingfilm, the carbon content in the organic silane type source gas needs tobe minimized when this coating serves as an insulating film whoseelectrical characteristics are important, such as a gate insulating filmor a part of a capacitor. The coating cannot be used as an insulatingfilm whose electrical characteristics are utilized unless the carboncontent is controlled.

[0012] Conventionally, where a film is formed by using an organic silanetype source gas such as ethyl orthosilicate, improving the step coveragenecessarily causes increase in hygroscopicity and carbon content, whichin turn causes reduction in reliability and degradation in semiconductorcharacteristics. If a large amount of oxygen is added to an organicsilane type gas such as ethyl orthosilicate to decrease the carboncontent, the step coverage is degraded and therefore voids, a break of awiring line, etc. may occur, which also cause reduction in reliabilityand degradation in semiconductor characteristics. In addition, an oxidefilm is more likely contaminated by impurities such as alkali metals.Once introduced, impurities behave as operative ions (movable ions) insome cases.

SUMMARY OF THE INVENTION

[0013] An object of the present invention is to enable formation of afilm which is superior in step coverage, lower in carbon content thanconventional films, low in hygroscopicity, and superior in impurityblocking performance.

[0014] Another object of the invention is to enable formation of a filmwhich is superior in step coverage, lower in carbon content thanconventional films, and low in hygroscopicity, with an increased filmforming rate.

[0015] To attain the above objects, according to one aspect of theinvention, there is provided a manufacturing method of a semiconductordevice having a step of forming an oxide film on a heated substrate byplasma CVD or atmospheric pressure CVD by using gases including anorganic silane type source gas and oxygen or a source gas includingozone that is generated from oxygen, wherein:

[0016] the oxide film is formed by adding hydrogen during formationthereof, and then converting said hydrogen into hydrogen radicals; or

[0017] the oxide film is formed by converting hydrogen into hydrogenradicals, and adding the hydrogen radicals during formation of the oxidefilm.

[0018] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on a heated substrate by plasma CVD or atmosphericpressure CVD by using gases including an organic silane type source gasand oxygen or a source gas including ozone that is generated fromoxygen, wherein:

[0019] the oxide film is formed by adding H₂O during formation thereof,and then generating hydrogen radicals from said H₂O.

[0020] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on at least part of a hydrophilic surface of a heatedsubstrate by atmospheric pressure CVD by using gases including anorganic silane type source gas and oxygen or a source gas includingozone that is generated from oxygen with an ozone density set at morethan 1%, wherein:

[0021] the oxide film is formed by adding hydrogen during formationthereof, and then converting said hydrogen into hydrogen radicals; or

[0022] the oxide film is formed by converting hydrogen into hydrogenradicals, and adding the hydrogen radicals during formation of the oxidefilm.

[0023] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on a heated substrate by plasma CVD by using gasesincluding an organic silane type source gas and oxygen or a source gasincluding ozone that is generated from oxygen, wherein:

[0024] an amount of said oxygen is less than 15 times an amount of theorganic silane type source gas; and

[0025] the oxide film is formed by adding hydrogen at an amount not lessthan 0.01 times the amount of the organic silane type source gas duringformation thereof, and then converting said hydrogen into hydrogenradicals.

[0026] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on a heated substrate by plasma CVD by using gasesincluding an organic silane type source gas and oxygen or a source gasincluding ozone that is generated from oxygen, wherein:

[0027] an amount of said oxygen is less than 15 times an amount of theorganic silane type source gas; and

[0028] the oxide film is formed by adding H₂O by bubbling H₂O with acarrier gas of an amount 0.1 to 1 times the amount of the organic silanetype source gas during formation of the oxide film, and then generatinghydrogen radicals from said H₂O.

[0029] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on a heated substrate by atmospheric pressure CVD by usinggases including an organic silane type source gas and oxygen or a sourcegas including ozone that is generated from oxygen, wherein:

[0030] the oxide film is formed by adding hydrogen at an amount not lessthan 0.1 times the amount of the organic silane type source gas duringformation thereof, and then converting said hydrogen into hydrogenradicals.

[0031] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on a heated glass substrate by plasma CVD or atmosphericpressure CVD by using gases including an organic silane type source gasand oxygen or a source gas including ozone that is generated from oxygenunder a semiconductor layer to become an active layer in a process offorming a thin-film transistor on the glass substrate, wherein:

[0032] the oxide film is formed by adding hydrogen during formationthereof, and then converting said hydrogen into hydrogen radicals; or

[0033] the oxide film is formed by converting hydrogen into hydrogenradicals, and adding the hydrogen radicals during formation of the oxidefilm.

[0034] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on a heated glass substrate by plasma CVD by using gasesincluding an organic silane type source gas and oxygen or a source gasincluding ozone that is generated from oxygen over a semiconductor layerto become an active layer in a process of forming a thin-film transistoron the glass substrate, wherein:

[0035] the oxide film is formed by adding hydrogen during formationthereof, and then converting said hydrogen into hydrogen radicals; or

[0036] the oxide film is formed by converting hydrogen into hydrogenradicals, and adding the hydrogen radicals during formation of the oxidefilm.

[0037] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on a heated glass substrate by plasma CVD or atmosphericpressure CVD by using gases including an organic silane type source gasand oxygen or a source gas including ozone that is generated from oxygenover a gate insulating film in a process of forming a thin-filmtransistor on the glass substrate, wherein:

[0038] the oxide film is formed by adding hydrogen during formationthereof, and then converting said hydrogen into hydrogen radicals; or

[0039] the oxide film is formed by converting hydrogen into hydrogenradicals, and adding the hydrogen radicals during formation of the oxidefilm.

[0040] According to still another aspect of the invention, there isprovided a plasma CVD apparatus for manufacture of a semiconductordevice, comprising:

[0041] a vacuum chamber;

[0042] parallel plate electrodes;

[0043] a plasma power source connected to a first one of the electrodesvia a matching device;

[0044] a substrate holder capable of being heated, for placing asubstrate having a film forming surface on a second one of theelectrodes; and

[0045] a pump connected to the vacuum chamber via a flow control valve,

[0046] wherein an organic silane type source gas and oxygen or oxygenpartially converted into ozone are introduced into the vacuum chambervia respective flow rate controllers through the first electrode; and

[0047] H₂O is introduced into the vacuum chamber together with a carriergas independently of the organic silane type source gas by bubblingwater in a tank with the carrier gas that is supplied via a flow ratecontroller.

[0048] According to another aspect of the invention, there is providedan atmospheric pressure CVD apparatus for manufacture of a semiconductordevice, comprising:

[0049] a substrate holder capable of being heated, for mounting asubstrate having a film forming surface; and

[0050] a gas nozzle so disposed as to be opposed to the film formingsurface of the substrate,

[0051] wherein an organic silane type source gas and a carrier gas aresupplied to the gas nozzle via a flow rate controller;

[0052] oxygen is supplied, via a flow rate controller, to an ozonizerfor converting part of said oxygen into ozone, and then supplied to thegas nozzle; and

[0053] hydrogen is supplied, via a flow rate controller, to a catalystfor converting part of said hydrogen into hydrogen radicals, and thensupplied to the gas nozzle.

[0054] To attain the above objects, according to a further aspect of theinvention, there is provided a manufacturing method of a semiconductordevice having a step of forming an oxide film on a heated substrate byplasma CVD or atmospheric pressure CVD by using material gases includingan organic silane type source gas and hydrogen or active hydrogen,wherein:

[0055] the oxide film is formed by adding nitrogen oxide expressed asN_(x)O_(y) during formation thereof.

[0056] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on a heated substrate by plasma CVD or atmosphericpressure CVD by using material gases including an organic silane typesource gas and H₂O, wherein:

[0057] the oxide film is formed by adding nitrogen oxide expressed asN_(x)O_(y) during formation thereof.

[0058] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on at least part of a hydrophilic surface of a heatedsubstrate by atmospheric pressure CVD by using material gases includingan organic silane type source gas, oxygen or a source gas includingozone that is generated from oxygen, and hydrogen or active hydrogenwith an ozone density set at more than 1%, wherein:

[0059] the oxide film is formed by adding nitrogen oxide expressed asN_(x)O_(y) during formation thereof.

[0060] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on a heated substrate by plasma CVD by using materialgases including an organic silane type source gas, oxygen or a sourcegas including ozone that is generated from oxygen, and hydrogen oractive hydrogen, wherein:

[0061] an amount of said oxygen or the source gas including ozonegenerated from oxygen is less than 15 times an amount of the organicsilane type source gas; and

[0062] said hydrogen or active hydrogen is added at an amount not lessthan 0.01 times the amount of the organic silane type source gas; and

[0063] the oxide film is formed by adding nitrogen oxide expressed asN_(x)O_(y) during formation thereof.

[0064] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on a heated substrate by plasma CVD by using materialgases including an organic silane type source gas, oxygen or a sourcegas including ozone that is generated from oxygen, and H₂O, wherein:

[0065] an amount of said oxygen or the source gas including ozonegenerated from oxygen is less than 15 times an amount of the organicsilane type source gas; and

[0066] said H₂O is added by bubbling H₂O with a carrier gas of an amount0.1 to 1 times the amount of the organic silane type source gas duringformation of the oxide film; and

[0067] the oxide film is formed by adding nitrogen oxide expressed asN_(x)O_(y) during formation thereof.

[0068] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on a heated substrate by atmospheric pressure CVD by usingmaterial gases including an organic silane type source gas and hydrogenor active hydrogen, wherein:

[0069] said hydrogen or active hydrogen is added at an amount not lessthan 0.1 times the amount of the organic silane type source gas; and

[0070] the oxide film is formed by adding nitrogen oxide expressed asN_(x)O_(y) during formation thereof.

[0071] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on a heated glass substrate by plasma CVD or atmosphericpressure CVD by using gases including an organic silane type source gasand hydrogen or active hydrogen under a semiconductor layer to become anactive layer in a process of forming a thin-film transistor on the glasssubstrate, wherein:

[0072] the oxide film is formed by adding nitrogen oxide expressed asN_(x)O_(y) during formation thereof.

[0073] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on a heated glass substrate by plasma CVD by using gasesincluding an organic silane type source gas and hydrogen or activehydrogen over a semiconductor layer to become an active layer in aprocess of forming a thin-film transistor on the glass substrate,wherein:

[0074] the oxide film is formed by adding nitrogen oxide expressed asN_(x)O_(y) during formation thereof.

[0075] According to another aspect of the invention, there is provided amanufacturing method of a semiconductor device having a step of formingan oxide film on a heated glass substrate by plasma CVD or atmosphericpressure CVD by using gases including an organic silane type source gasand hydrogen or active hydrogen over a gate insulating film in a processof forming a thin-film transistor on the glass substrate, wherein:

[0076] the oxide film is formed by adding nitrogen oxide expressed asN_(x)O_(y) during formation thereof.

[0077] According to another aspect of the invention, in the abovemanufacturing methods of a semiconductor device, the organic silane typesource gas is one of TEOS, OMCTS, and HMDS.

[0078] According to another aspect of the invention, in the abovemanufacturing methods of a semiconductor device, the organic silane typesource gas is a material including fluorine.

[0079] According to another aspect of the invention, in the abovemanufacturing methods of a semiconductor device, the nitrogen oxideexpressed as N_(x)O_(y) is one selected from the group consisting ofN₂O, NO, N₂O₃, NO₂, N₂O₄, N₂O₅, NO₃ and N₂O₆.

[0080] According to another aspect of the invention, in the abovemanufacturing methods of a semiconductor device, a content of carbonexpressed as C of the oxide film as measured by SIMS has a minimum valueof less than 3×10¹⁹ cm⁻³ in a depth-direction profile, and a content ofnitrogen expressed as N of the oxide film as measured by SIMS has amaximum value of more than 1×10¹⁹ cm⁻³ in a depth-direction profile.

[0081] The present assignee previously used a mixture of oxygen andethyl orthosilicate in forming an oxide film by plasma CVD by usingethyl orthosilicate. As a result of various experiments to find a propermethod for reducing the carbon content of a film formed, the inventorshave found that it is effective to use hydrogen radicals, hydrogen ions,etc. during the film formation. Active hydrogen such as hydrogenradicals and hydrogen ions gasify carbon by reacting with it and formingCH_(x). It is possible to eliminate carbon during film formationparticularly by cutting carbon single bonds C—C to produce CH₄ and C—OH.

[0082] Hydrogen has a stronger decarbonization effect than oxygen.Further, since the hydrogen atom is small, the sputtering effect ofhydrogen ions on a film and a substrate is almost negligible. Therefore,in forming a film by plasma CVD by mixing an organic silane type sourcegas, nitrogen oxide, and hydrogen, the mixing ratio of the organicsilane type source gas and nitrogen oxide is so determined as to providea film forming rate that enables superior step coverage and highproductivity and hydrogen is mixed for decarbonization. In particular,the above effects are remarkable when hydrogen is introduced by anamount 0.1 to 1 times the amount of the organic silane type source gas.Plasma-generated precursors from the organic silane source gas, oxygenions, ozone, and oxygen radicals repeat film forming surface reaction onthe substrate surface. In this operation, the precursors flow above thesubstrate surface while transforming into various type of precursors, toform an oxide film having superior step coverage. While the oxide filmis formed by reaction among the precursors, oxygen ions, ozone, andoxygen radicals, hydrogen ions and hydrogen radicals gasify carbon byreacting with carbon atoms on the substrate surface. Gasified carbon isexhausted by a vacuum pump.

[0083] If it is possible to dope an oxide film with nitrogen at the sametime as reduce carbon contained therein, the advantages of both of anoxide film and a nitride film can be obtained. In particular, in forminga nitrogen-doped oxide film by using an organic silane type source gassuch as ethyl orthosilicate, both oxygen and nitrogen can be supplied toa film during film formation by using nitrogen oxide (N_(x)O_(y) ,compound of nitrogen and oxygen) such as N₂O, NO, N₂O₃, NO₂, N₂O₄, N₂O₅,NO₃ and N₂O₆. A nitrogen-doped oxide film is much superior in waterresistance and impurity blocking performance to a non-doped oxide film.In particular, alkali metals such as Na and K become operative ionsmoving through an oxide film, which is a major cause of unstableelectrical properties of a semiconductor. A nitrogen-doped oxide film isgiven much improved blocking performance compared to a non-doped oxidefilm, and therefore can suppress the operability of alkali metals suchas Na and K.

[0084] The characteristics of a nitrogen-doped oxide film can be variedby properly selecting the molecular weight of nitrogen oxide inaccordance the intended characteristics and adding oxygen when it isinsufficient.

[0085] Since nitrogen oxide consists of nitrogen and oxygen that arecombined in advance, an oxide film formed is easily combined, i.e.,doped with nitrogen when nitrogen oxide reacts with an organic silanetype source gas. A nitrogen-doped oxide film can be formed by usingammonia or a mixture of nitrogen and oxygen instead of nitrogen oxide.However, since relatively large energy is needed to decompose ammonia,the film forming surface of a substrate may be seriously damaged in aplasma method or the like. Further, since nitrogen is hardly combinedwith other molecules, it is difficult to control the dope amount. Thus,it is very effective to use nitrogen oxide to dope an oxide film withnitrogen when it is formed by using an organic silane type source gas.

[0086] Where the invention is applied to film formation by atmosphericpressure CVD, a catalyst method is used to partly convert hydrogen intohydrogen radicals. Proper examples of the catalyst include 3d-transitionmetals such as platinum, palladium, reduced nickel, cobalt, titanium,vanadium, and tantalum; compounds of metals such as aluminum, nickel,platinum-silicon, platinum-chlorine, platinum-rhenium,nickel-molybdenum, and cobalt-molybdenum; and mixtures or compounds ofany of the above transition metals and alumina or silica gel. Inaddition, Raney catalysts of cobalt, ruthenium, palladium, nickel, andthe like, and mixtures or compounds of any of those Raney catalysts andcarbon can be used. These catalysts are used in a granulated, reticular,or powder state. Materials having a low melting point and markedlyincreasing the initial absorption rate of a reactive substance, andmaterials containing alkali metals such as sodium which easily vaporizeare not suitable for the catalyst. Examples of such unfavorablematerials are copper and tungsten. Experiments revealed considerabledegradation of the catalyst at a temperature higher than thedecomposition temperature of a reactive substance. The amount and thedensity of the catalyst depend on the effective contact area with areactive gas, and may be adjusted when necessary. Active hydrogenradicals are generated by passing hydrogen through the catalyst beingheated. Active ozone is generated by passing oxygen through an ozonizer.

[0087] In forming a SiO_(x) film by using an atmospheric pressure CVDapparatus in which a substrate is heated, organic silane such as ethylorthosilicate in a tank is bubbled with a carrier gas such as nitrogen.Oxygen is introduced into the apparatus while being partly convertedinto ozone in passing through the ozonizer. Hydrogen is introduced intothe apparatus through the catalyst.

[0088] Where nitrogen oxide is added to a SiO_(x) film, organic silanein a tank is bubbled with a carrier gas such as a carrier gas ofnitrogen oxide (N_(x)O_(y)) such as NO, NO₂ or N₂O. Oxygen is introducedinto the apparatus while being partly converted into ozone in passingthrough the ozonizer. Hydrogen is introduced into the apparatus throughthe catalyst.

[0089] All gases are supplied to the substrate in a mixed state from agas nozzle having a dispersing mechanism. In forming a film byatmospheric pressure CVD by using only ethyl orthosilicate and ozone, anoxide film is formed much differently depending on whether the surfaceof a substrate is hydrophilic or hydrophobic. While a normal film can beformed on a substrate having a hydrophobic surface, abnormal filmformation or reduction in film forming rate likely occurs with ahydrophilic surface. There occurs problems when an oxide film is formedon at least part of a hydrophilic surface. In contrast, the invention,which is associated with the use of hydrogen radicals, can not onlyprovide the impurity blocking effect but also prevent abnormal filmformation and reduction in film forming rate because active hydrogenterminates the substrate surface to thereby create a hydrophobicsurface. In particular, these effects are remarkable when hydrogen isintroduced by an amount 0.1 to 1 times the amount of a carrier gas suchas nitrogen. Where ethyl orthosilicate is directly gasified by heatingit, these effects are enhanced by a factor of 1 to 5.

[0090] Where nitrogen oxide is added to a SiO_(x) film, nitrogen oxidecan be used as a carrier gas. Similar effects can be obtained by using,as a carrier gas, nitrogen or the like rather than nitrogen oxide andintroducing nitrogen oxide by a separate system.

[0091] Although in the above description hydrogen radicals are generatedby plasma in plasma CVD and by a catalyst method in atmospheric pressureCVD, they may be generated in opposite manners. That is, active hydrogenradicals may be generated in advance by a catalyst method and thenintroduced into a plasma CVD apparatus. It is also possible to generateactive hydrogen radicals in advance by discharging and then mix thosewith other gases by a gas nozzle of an atmospheric pressure CVDapparatus.

[0092] Where an oxide film is formed by using an organic silane typesource gas, an oxygen source gas is used because active oxygen radicals,oxygen ions, and ozone are necessarily used. In the invention, H₂O maybe used to additionally use active hydrogen radicals or hydrogen ions.However, since H₂O and an organic silane source gas react with eachother very actively, there is a possibility that a pipe may be cloggedif they are mixed with each other in the pipe before their reaction on asubstrate. It is preferable that in a plasma CVD apparatus the pipes forintroducing an organic silane source gas and H₂O are separatelyprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0093]FIG. 1 shows a parallel plate plasma CVD apparatus used in firstand second embodiments of the present invention;

[0094]FIG. 2 illustrates a method of evaluating the step coverage;

[0095]FIGS. 3A and 3B show measurement data of oxide films formedaccording to the invention;

[0096]FIG. 4 shows an atmospheric pressure CVD apparatus used in thirdand fourth embodiments of the invention;

[0097] FIGS. 5A-5F shows a TFT manufacturing process according to fifthand sixth embodiments of the invention; and

[0098]FIG. 6 shows how metal wiring lines are buried according toseventh and eighth embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0099] Embodiment 1

[0100]FIG. 1 shows a parallel plate plasma CVD apparatus that is used topractice the present invention. A vacuum chamber 11 capable of beingevacuated accommodates a cathode 12 that also serves as a gas showerhead, a substrate 13 for film formation, and an anode 14 having a roleof a substrate holder that incorporates a heater and hence can heat thesubstrate 13. A pump 15 for evacuating the vacuum chamber 11 andexhausting an unnecessary gas is coupled to the vacuum chamber 11 aroundthe anode 14. A control valve 16 for controlling the pressure of thevacuum chamber 11 approximately at a constant value is provided betweenthe vacuum chamber 11 and the pump 15. A plasma power supply 18 isconnected to the cathode 12 via a matching device 17.

[0101] In this embodiment, film forming source gases 19 of organicsilane 19 a and oxygen 19 b are supplied to the cathode 12 via flow ratecontrollers 20, that is, an organic silane flow rate controller 20 a andan oxygen flow rate controller 20 b. Decarbonization source gases 21 ofhydrogen 21 a and a decarbonization carrier gas 21 b can be introducedinto the chamber 11 via decarbonization source gas flow rate controllers22, that is, a hydrogen flow rate controller 22 a and a carrier gas flowrate controller 22 b. The decarbonization carrier gas 21 b is allowed tobubble H₂O 23 that is contained in a water tank 24. Only this system isseparated from the other gas systems and directly connected to thevacuum chamber 11 to prevent the pipe from being clogged due to reactionof ethyl orthosilicate and H₂O.

[0102] The cathode 12 incorporates an agitation mechanism such as adispersing plate to allow gases to be applied uniformly onto the surfaceof the substrate 13. Since organic silane 19 a assumes liquid form atthe ordinary temperature and in many cases has an insufficient vaporpressure, some measure is needed to prevent organic silane 19 a fromcohering between its tank and the vacuum chamber 11. For example,organic silane in the tank is bubbled with an inert gas (carrier gas)such as He, Ne or Ar. Alternatively, the tank is heated to increase thevapor pressure of the organic silane source gas and the pipe from thetank to the vacuum chamber 11 is heated to a temperature higher thanthat of the tank.

[0103] After the vacuum chamber 11 was evacuated, the substrate 13 washeated to 200-500° C. by the heater that was incorporated in the anode14. If the substrate temperature is too low, the density of a resultingfilm becomes so low as to be almost unusable as a film for asemiconductor. Typically, the substrate temperature was set at 300-350°C. Ethyl orthosilicate was used as organic silane 19 a. In a state thatthe tank of ethyl orthosilicate was heated to 80° C. and the entire pipefrom the tank to the vacuum chamber 11 was heated to 90° C., ethylorthosilicate was introduced into the vacuum chamber 11 while its flowrate was controlled by the organic silane flow rate controller 20 a.Hydrogen 21 a was used as the decarbonization source gas 21.

[0104] The power supplied from the plasma power supply 18 was 0.1-1.5W/cm², typically 0.2-0.5 W/cm². The reaction pressure was set at 0.1-3Torr, typically 0.8-1.5 Torr. The gases were supplied at a ratio (ethylorthosilicate):oxygen:hydrogen=1:1-15:0-10. The interval between thecathode 12 and the anode 13 was set at 30-150 mm, typically 70 mm.

[0105] Further, without using any decarbonization source gas 21, oxidefilms were formed with supply ratios (ethyl orthosilicate):oxygen=1:1,1:3, 1:5, 1:10 and 1:15. The other conditions were such that thesubstrate temperature was 300-350° C., the supply power was 0.2-0.5W/cm², the electrode interval was 70 mm, and the reaction pressure was0.8-1.5 Torr. Table 1 shows results of the step coverage, the carboncontent, and the hygroscopicity of the respective cases. TABLE 1 Gassupply ratio 1:1 1:3 1:5 1:10 1:15 Step 1.0 1.0 0.8 0.6 0.2 coverageCarbon con- 6 × 10²¹ 7 × 10²⁰ 6 × 10¹⁹ 1 × 10¹⁹ 7 × 10¹⁸ tent (cm⁻³)Hygroscopi- 10 7 1 0.1 0 city ratio

[0106] Referring to FIG. 2, the step coverage is defined by b/a. In FIG.2, a step pattern 25 formed on a substrate 13 is covered with an oxidefilm 26. The step pattern 25 was formed by depositing aluminum at athickness of 1 μm and then patterning it into lines having a width of 1μm. Symbol b means a minimum thickness of the oxide film 26 adjacent tothe side face of the step pattern 25, and a means a thickness of theoxide film 26 at a position sufficiently distant (about 3 μm inmeasurements) from the step pattern 25. The carbon content is defined asa minimum of carbon concentration values in terms of the number ofcarbon atoms per cubic centimeters as measured in the depth direction ofthe oxide film 26 to the substrate surface by secondary ion massspectrometry. The hygroscopicity ratio is defined such that an increasefrom the initial value of a peak absorption value in the vicinity of3,660 cm⁻¹ when an oxide film is left for 12 hours in an atmosphere of25° C. and humidity of 60% RH is divided by a film thickness in nm andthen multiplied by a certain constant (normalized). Although the abovedefinition of the hygroscopicity ratio is not a universal one, itenables comparison among samples.

[0107] As clearly seen from Table 1, as the ratio of oxygen to ethylorthosilicate is increased, the step coverage degrades, the carboncontent decreases, and the hygroscopicity lowers.

[0108] Table 2 shows results of an experiment in which the supply ratioof hydrogen to ethyl orthosilicate ratio was set at 0.01, 0.05, 0.1,0.2, 0.5 and 0.8. TABLE 2 Hydrogen ratio 0.01 0.05 0.1 0.2 0.5 0.8 1:1Step 1 1 1 1 1 1 coverage Carbon 2 × 10²¹ 8 × 10²⁰ 1 × 10²⁰ 8 × 10¹⁹ 6 ×10¹⁹ 6 × 10¹⁹ content (cm⁻³) Hygrosc- 10 5 2.5 1.4 1 1 opicity ratio 1:3Step 1 1 1 1 1 1 coverage Carbon 7 × 10²⁰ 4 × 10²⁰ 7 × 10¹⁹ 4 × 10¹⁹ 2 ×10¹⁹ 2 × 10¹⁹ content (cm⁻³) Hygrosc- 7 4.5 2 1 0.7 0.7 opicity ratio1:5 Step 0.8 0.8 0.8 0.8 0.8 0.8 coverage Carbon 4 × 10¹⁹ 2 × 10¹⁹ 1 ×10¹⁹ 8 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ content (cm⁻³) Hygrosc- 0.9 0.6 0.3 0.20.1 0.1 opicity ratio 1:10 Step 0.6 0.6 0.6 0.6 0.6 0.6 coverage Carbon1 × 10¹⁹ 8 × 10¹⁸ 7 × 10¹⁸ 6 × 10¹⁸ 5 × 10¹⁸ 5 × 10¹⁸ content (cm⁻³)Hygrosc- 0.1 0.08 0.04 0 0 0 opicity ratio 1:15 Step 0.2 0.2 0.2 0.2 0.20.2 coverage Carbon 7 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 5 × 10¹⁸ 4 × 10¹⁸ 4 ×10¹⁸ content (cm⁻³) Hygrosc- 0 0 0 0 0 0 picity ratio

[0109] While the addition of hydrogen of only 0.01 affects all thecharacteristics concerned, the addition of hydrogen exceeding 0.5 doesnot change the characteristics. In particular, the addition of hydrogencan reduce the carbon content and improve the hygroscopicity whilecausing almost no change in step coverage. Further, it is understoodthat where oxygen is introduced by an amount 15 times that of ethylorthosilicate, the addition of hydrogen has almost no effects.Therefore, it is concluded that the invention becomes effective when thesupply ratio of oxygen to ethyl orthosilicate is less than 15 and thesupply ratio of hydrogen to ethyl orthosilicate is not less than 0.01.

[0110] Similar results were obtained by introducing H₂O instead ofhydrogen. By setting the supply ratio of oxygen to ethyl orthosilicateless than 15 and setting the supply ratio of a carrier gas for bubblingH₂O to ethyl orthosilicate in a range of 0.1 to 1, the carbon contentwas reduced and the hygroscopicity was improved without causing almostno change in step coverage. However, in the case of adding H₂O whichalso contains oxygen, excessive addition thereof changes the stepcoverage unlike the case of adding hydrogen. Therefore, there is acertain upper limit in the amount of added H₂O.

[0111] Embodiment 2

[0112] This embodiment is directed to a case of adding N_(x)O_(y) whileforming an oxide film by using the parallel plate plasma CVD apparatus,which was also used in the first embodiment. In this embodiment, as forfilm forming source gases 19, ethyl orthosilicate is used as an organicsilane type source gas 19 a and N₂O 19 b is also used. The film formingsource gases 19 a and 19 b are supplied to a cathode 12 via film formingflow rate controllers 20, that is, an ethyl orthosilicate flow ratecontroller 20 a and an N₂O flow rate controller 20 b. The componentsgiven the other reference symbols are the same as the correspondingcomponents in the first embodiment.

[0113] As described in the first embodiment, since organic silane 19 aassumes liquid form at the ordinary temperature and in many cases has aninsufficient vapor pressure, some measure is needed to prevent organicsilane 19 a from cohering between its tank and the vacuum chamber 11.Where nitrogen oxide is added as in this embodiment, one method is tobubble organic silane in the tank with an inert gas (carrier gas) suchas He, Ne or Ar. Alternatively, nitrogen oxide may be bubbled to have itserve both as a carrier gas and as a source gas of nitrogen and oxygen.

[0114] Film formation was performed in the following manner. After thevacuum chamber 11 was evacuated, the substrate 13 was heated to 200-500°C. by the heater that was incorporated in the anode 14. If the substratetemperature is too low, the density of a resulting film becomes so lowas to be almost unusable as a film for a semiconductor. Typically, thesubstrate temperature was set at 300-350° C. In a state that the tank ofethyl orthosilicate was heated to 80° C. and the entire pipe from thetank to the vacuum chamber 11 was heated to 90° C., ethyl orthosilicatewas introduced into the vacuum chamber 11 while its flow rate wascontrolled by the ethyl orthosilicate flow rate controller 20 a.Hydrogen 21 a was used as the decarbonization source gas 21.

[0115] The power supplied from the plasma power supply 18 was 0.1-1.5W/cm², typically 0.2-0.5 W/cm². The reaction pressure was set at 0.1-3Torr, typically 0.8-1.5 Torr. The gases were supplied at a ratio (ethylorthosilicate):N₂O:hydrogen=1:1-15:0-1. The interval between the cathode12 and the anode 13 was set at 30-150 mm, typically 70 mm.

[0116] While the addition of hydrogen of only 0.01 affects all thecharacteristics concerned, the addition of hydrogen exceeding 0.5 doesnot change the characteristics. In particular, the addition of hydrogencan reduce the carbon content and improve the hygroscopicity whilecausing almost no change in step coverage. Further, it is understoodthat where N₂O is introduced by an amount 15 times that of ethylorthosilicate, the addition of hydrogen has almost no effects.Therefore, it is concluded that the invention becomes effective when thesupply ratio of N₂O to ethyl orthosilicate is less than 15 and thesupply ratio of hydrogen to ethyl orthosilicate is not less than 0.01.Almost the same effects were obtained when NO, NO₂, or the like was usedinstead of N₂O.

[0117]FIGS. 3A and 3B are data of various characteristics showing theeffects of hydrogen and N₂O. FIG. 3A shows the carbon content that wasobtained when the supply ratio of ethyl orthosilicate to N₂O was fixedat 1:5 and the added amount of hydrogen was varied. The vertical axisrepresents the carbon content as defined by the minimum carbon contentin an oxide film in a depth-direction profile obtained by SIMS(secondary ion mass spectrometry). The horizontal axis the supply ratioof hydrogen to ethyl orthosilicate. It is seen that the carbon contentin an oxide film can be reduced by slightly adding hydrogen, and thatthe carbon content approximately saturates with respect to the hydrogenratio in the hydrogen ratio range larger than 0.5. When the hydrogenratio is 0.5, a minimum content of carbon in the depth-direction profileis about 3×10¹⁹ cm⁻³. The minimum carbon content is smaller than thisvalue when the hydrogen ratio is larger than 0.5, and is larger thanthis value when the hydrogen ratio is smaller than 0.5. Although theadded amount of hydrogen varies with process conditions, the above valueof carbon content serve as one measure.

[0118]FIG. 3B shows results of what is called BT tests (measurements ofmovement of operative ion charges by means of a MOS capacitor) performedin a case where the supply ratio of ethyl orthosilicate to hydrogen wasfixed at 1:0.5 and the added amount of N₂O was varied, and in a casewhere oxygen was used instead of N₂O. A 1,000-Å-thick oxide film wasformed on a substrate of a P-type silicon wafer by using N₂O or oxygen,and a MOS capacitor was formed by depositing aluminum on the oxide filmand the back surface of the substrate by evaporation. In thisevaporating operation, electrodes containing alkali metals wereintentionally formed by depositing aluminum by resistance heating bymeans of a tungsten coil. Annealing was performed at 120° C. for 30minutes in a nitrogen atmosphere while a voltage was applied to the topelectrode of the MOS capacitor to produce 1 MV/cm. After the temperaturewas reduced to the room temperature, the capacitance of the MOScapacitor was measured at low and high frequencies and a flat-bandvoltage (+V_(FB)) was calculated. Then, annealing was again performed at120° C. for 30 minutes in a nitrogen atmosphere while −1 MV/cm wasapplied. After the temperature was reduced to the room temperature, thecapacitance of the MOS capacitor was measured at low and highfrequencies and a flat-band voltage (−V_(FB)) was calculated. Theabsolute value of a difference between +V_(FB) and −V_(FB) is denoted byΔV_(FB) and used as the vertical axis of FIG. 3B.

[0119] The horizontal axis represents the ratio of N₂O or oxygen toethyl orthosilicate.

[0120] In the case of using oxygen instead of N₂O, ΔV_(FB) is large overthe entire range of the added amount of oxygen except for a slightdecrease in a range where the oxygen amount is small. On the other hand,in the case of using N₂O, ΔV_(FB) decreases as the added amount of N₂Oincreases, and saturates when the ratio of N₂O to ethyl orthosilicate islarger than 5. When ΔV_(FB) is large, alkali metals in the oxide filmare moved by an electric field applied thereto. It is seen that the useof N₂O has a remarkable effect. It has been found that the step coverageis degraded when the supply ratio of N₂O to ethyl orthosilicate islarger than 15. Nitrogen contents were measured by SIMS in a case whereN₂O was supplied by an amount 5 times that of ethyl orthosilicate, tofind that the maximum content of nitrogen (N) in the depth direction wasabout 1×10¹⁹ cm⁻³. It was also confirmed that the maximum content wassmaller than the above value when the N₂O ratio is smaller than 5, andwas larger than the above value when the N₂O content is larger than 5.Although the mixing ratio varies with parameters X and Y in a molecularformula N_(x)O_(y) of nitrogen oxide, in terms of characteristics themaximum nitrogen (N) content value of about 1×10¹⁹ cm⁻³ in the depthdirection serves as one measure.

[0121] Similar results were obtained by introducing H₂O instead ofhydrogen. By setting the supply ratio of N₂O to ethyl orthosilicate lessthan 15 and setting the supply ratio of a carrier gas for bubbling H₂Oto ethyl orthosilicate in a range of 0.1 to 1, the carbon content wasreduced and the hygroscopicity was improved without causing almost nochange in step coverage. However, in the case of adding H₂O which alsocontains oxygen, excessive addition thereof changes the step coverageunlike the case of adding hydrogen. Therefore, there is a certain upperlimit in the amount of added H₂O; the step coverage is degraded if theratio of the carrier gas to ethyl orthosilicate is larger than unity.

[0122] Embodiment 3

[0123] This embodiment is directed to a case of forming an oxide film byusing an atmospheric pressure CVD apparatus shown in FIG. 4.

[0124] A substrate 31 is placed on a substrate holder 32 incorporating aheater. In this embodiment, a gas nozzle 33 incorporating a gasdispersing system is so constructed as to be capable of reciprocalmovement (indicated by arrow 34) above the substrate 31. The gas nozzle33 need not always be provided with a mechanism of allowing filmformation with its reciprocal movement as in this embodiment, but may befixed in a state of allowing uniform gas supply over the entire surfaceof the substrate 31. As a further alternative, the apparatus may beconstructed such that the gas nozzle 33 is fixed while the substrateholer 32 is moved. Further, although in this embodiment the substrate 31is located under the gas nozzle 33 and the film-forming surface isdirected upward (face-up arrangement), the substrate 31 may be locatedabove the gas nozzle 33 so that the film-forming surface is directeddownward (face-down arrangement), in which case the gas nozzle 33supplies gases to the substrate 31 from below.

[0125] As for the gas system, an organic silane type source gas 35 issupplied to the gas nozzle 33 via an organic silane type gas flow ratecontroller 39. Oxygen 36 is supplied to ozonizer 43 via an oxygen flowrate controller 40, and then supplied to the gas nozzle 33. Hydrogen 38is supplied to a catalyst 44 via a hydrogen flow rate controller 42.Further, a nitrogen oxide source gas 45 (used in the fourth embodiment)is supplied to the gas nozzle 33 via a nitrogen oxide flow ratecontroller 46.

[0126] The ozonizer 44 effectively generates ozone from oxygen. Acarrier gas 37 is supplied to the gas nozzle 33 via a carrier gas flowrate controller 41. In this system, the vapor pressure of an organicsilane type gas is increased by heating a tank containing it, and isdirectly controlled by the organic silane type gas flow rate controller39. Alternatively, it is also effective to bubble an organic silane typematerial in a tank with a gas such as nitrogen or helium and use aresulting gas as the organic silane type source gas 35.

[0127] Proper examples of the catalyst 44 include 3d-transition metalssuch as platinum, palladium, reduced nickel, cobalt, titanium, vanadium,and tantalum; compounds of metals such as aluminum, nickel,platinum-silicon, platinum-chlorine, platinum-rhenium,nickel-molybdenum, and cobalt-molybdenum; and mixtures or compounds ofany of the above transition metals and alumina or silica gel. Inaddition, Raney catalysts of cobalt, ruthenium, palladium, nickel, andthe like, and mixtures or compounds of any of those Raney catalysts andcarbon can be used. These catalysts are used in a granulated, reticular,or powder state. Materials having a low melting point and markedlyincreasing the initial absorption rate of a reactive substance, andmaterials containing alkali metals such as sodium which easily vaporizeare not suitable for the catalyst 44. Examples of such unfavorablematerials are copper and tungsten.

[0128] Experiments revealed considerable degradation of the catalyst 44at a temperature higher than the decomposition temperature of a reactivesubstance.

[0129] The amount and the density of the catalyst 44 depend on theeffective contact area with a reactive gas, and may be adjusted whennecessary. When hydrogen is passed through the catalyst 44 being heated,hydrogen is partly converted into active hydrogen radicals. In thisembodiment, the catalyst 44 was formed such that platinum (15 wt %) wasmixed into alumina and a mixture was granulated.

[0130] The substrate 31 was heated to 300-500° C., typically 300-400° C.Ethyl orthosilicate, OMCTS (octamethylcyclotetrasiloxane), HMDS(hexamethyldisiloxane), and the like were used as the organic silanesource gas 35. Typically, ethyl orthosilicate was used. Helium,nitrogen, and the like were used as the carrier gas 37. Typically,helium was used. Table 3 shows results of the step coverage, the carboncontent, and the hygroscopicity of respective cases where the ratio ofthe flow rate of hydrogen 38 to that of the organic silane source gas 35were set at 0, 0.1, 0.2, 0.5 and TABLE 3 Hydrogen ratio 0 0.1 0.2 0.5 1Step 1 1 1 1 1 coverage Carbon con- 4 × 10²¹ 1 × 10²¹ 4 × 10²⁰ 8 × 10¹⁹8 × 10¹⁹ tent (cm⁻³) Hygroscopi- 8.0 7.5 6.0 5.0 4.9 city ratio

[0131] Referring to FIG. 2, the step coverage is defined by b/a. In FIG.2, a step pattern 25 formed on a substrate 13 is covered with an oxidefilm 26. The step pattern 25 was formed by depositing aluminum at athickness of 1 μm and then patterning it into lines having a width of 1μm. Symbol b means a minimum thickness of the oxide film 26 adjacent tothe side face of the step pattern 25, and a means the thickness of theoxide film 26 at a position sufficiently distant (about 3 μm inmeasurements) from the step pattern 25. The carbon content is defined asa minimum of carbon concentration values in terms of the number ofcarbon atoms per cubic centimeters as measured in the depth direction ofthe oxide film 26 to the substrate surface by secondary ion massspectrometry. The hygroscopicity ratio is defined such that an increasefrom the initial value of a peak absorption value in the vicinity of3,660 cm⁻¹ when an oxide film is left for 12 hours in an atmosphere of25° C. and humidity of 60% RH is divided by a film thickness in nm andthen multiplied by a certain constant (normalized). Although the abovedefinition of the hygroscopicity ratio is not a universal one, itenables comparison among samples.

[0132] Table 3 clearly shows effects of hydrogen radicals generated fromhydrogen 38 that was mixed through the catalyst 44. The carbon contentis reduced and the hygroscopicity is improved as the mixed amount ofhydrogen 38 with respect to the amount of the organic silane source gas35 is increased to 0.5. It is concluded from these results that theeffects of hydrogen radicals are remarkable when the ratio of hydrogen38 to the organic silane source gas 35 is in a range of 0.1-0.5, andthat they saturate even if hydrogen 38 is mixed at a ratio larger than0.5 though they do not degrade. That is, the carbon content can bereduced by adding hydrogen radicals generated by a catalyst method tothe organic silane/ozone type film formation according to atmosphericpressure CVD.

[0133] Embodiment 4

[0134] This embodiment is directed to a case of forming an oxide filmwhile adding nitrogen oxide by using the atmospheric pressure CVDapparatus shown in FIG. 4.

[0135] The substrate 31 was heated to 300-500° C., typically 300-400° C.Ethyl orthosilicate, OMCTS (octamethylcyclotetrasiloxane), HMDS(hexamethyldisiloxane), and the like were used as the organic silanesource gas 35. Typically, HMDS was used. Helium, nitrogen, and the likewere used as the carrier gas 37. Typically, helium was used.

[0136] In this embodiment, the vapor pressure of HMDS is increased byheating a tank containing it, and is directly controlled by the HMDSflow rate controller 39. Alternatively, it is effective to bubble HMDSin a tank with a gas such as nitrogen or helium and use a resulting gasas HMDS 35. It is also effective to bubble HMDS with NO₂.

[0137] Further, N_(x)O_(y) is added to an oxide film by introducing NO₂as nitrogen oxide 45.

[0138] The other components given the same reference numerals as thecorresponding components in the third embodiment have the sameconfigurations and functions as the latter.

[0139] A completed oxide film doped with nitrogen exhibited stableelectrical characteristics as, for instance, a capacitor when a minimumvalue in a depth-direction profile of the carbon concentration in thefilm as measured by SIMS (secondary ion mass spectrometry) was less thanabout 3×10¹⁹ cm⁻³. The nitrogen concentration to establish such acondition was attained by adding NO₂ by an amount more than 0.1 timesthe amount of HMDS. A completed oxide film doped with nitrogen exhibitedan alkali metal blocking effect when a maximum value in adepth-direction profile of the carbon concentration in the film asmeasured by SIMS (secondary ion mass spectrometry) was more than about1×10¹⁹ cm⁻³. The nitrogen concentration to establish such a conditionwas attained by adding NO₂ by an amount more than 5 times the amount ofHMDS.

[0140] Embodiment 5

[0141] This embodiment is directed to a case of applying this inventionto formation of a thin-film transistor (hereinafter also called TFT) byusing polysilicon.

[0142] FIGS. 5A-5F show a manufacturing process of a TFT.

[0143]FIG. 5A shows a step of forming an undercoat film 402 on a glasssubstrate 401. The glass substrate 401 was of a type made of a materialthat is highly transparent with respect to visible light, such asborosilicate glass or quartz. In this embodiment, Corning 7059 glassproduced by Corning Glass Works was used.

[0144] The invention was used in forming the undercoat film 402. If thechannel is of an N-type, electrons flow through it as carriers. If thechannel is of a P-type, holes flow through it as carriers. Aftercompletion of a TFT, there may occur an event that as the gate voltageis increased in the on-direction, a region like a channel of an oppositetype is formed under the true channel, i.e., on the side of thesubstrate 401.

[0145] If the channel is in an on state, the drain current shouldsaturate with an increase of the gate voltage. However, at a time pointwhen a channel of an opposite type occurs under the true channel, i.e.,on the side of the substrate 401, the drain current abruptly increasesto form a step in the gate voltage vs. drain current characteristic(what is called a kink effect). The kink effect can be prevented orreduced in possibility by applying the invention in forming theundercoat film 402. The possibility of occurrence of the kink effect islow if the undercoat film 402 is a SiO_(x) film that is free ofimpurities.

[0146] The undercoat film 402 was formed by using a parallel plateplasma CVD apparatus and gases of ethyl orthosilicate (also calledTEOS), oxygen and hydrogen. Other types of organic silane such as OMCTS(octamethylcyclotetrasiloxane) and HMDS (hexamethyldisiloxane) may beused effectively instead of ethyl orthosilicate. The substratetemperature was increased to 200-500° C., typically 400° C., and thefilm forming pressure was set at 0.1-2 Torr, typically 1 Torr. Thefrequency of a plasma power supply was made a high frequency of 5-50MHz, typically 20 MHz, and its power was set at 0.1-2 W/cm², typically0.3 W/cm². The supply ratio of ethyl orthosilicate to oxygen was set at1:5-20, typically 1:5. The amount of hydrogen was set in a range of(ethyl orthosilicate):hydrogen=1:0.01-1, typically at 1:0.5. Theundercoat film 402 was formed at a thickness of 500-3,000 Å, typically2,000 Å.

[0147] In forming an oxide film such as the undercoat film 402 by usingorganic silane, it is very effective to eliminate carbon from the filmby means of hydrogen radicals and hydrogen ions in any plasma CVD methodincluding the parallel plate plasma CVD method.

[0148] In the case of forming the undercoat film 402 by atmosphericpressure CVD, it is also possible to eliminate carbon during the filmformation by generating hydrogen radicals by a catalyst method and usingthose during the film formation. Thus, the invention can effectively beapplied to atmospheric pressure CVD using organic silane.

[0149] In the case of applying the invention to film formation byatmospheric pressure CVD, a catalyst method is used to convert hydrogento hydrogen radicals. Proper examples of the catalyst include3d-transition metals such as platinum, palladium, reduced nickel,cobalt, titanium, vanadium, and tantalum; compounds of metals such asaluminum, nickel, platinum-silicon, platinum-chlorine, platinum-rhenium,nickel-molybdenum, and cobalt-molybdenum; and mixtures or compounds ofany of the above transition metals and alumina or silica gel. Inaddition, Raney catalysts of cobalt, ruthenium, palladium, nickel, andthe like, and mixtures or compounds of any of those Raney catalysts andcarbon can be used. These catalysts are used in a granulated, reticular,or powder state. Materials having a low melting point and markedlyincreasing the initial absorption rate of a reactive substance, andmaterials containing alkali metals such as sodium which easily vaporizeare not suitable for the catalyst 44. Examples of such unfavorablematerials are copper and tungsten.

[0150] Experiments revealed considerable degradation of a catalyst at atemperature higher than the decomposition temperature of a reactivesubstance.

[0151] The amount and the density of a catalyst depend on the effectivecontact area with a reactive gas, and may be adjusted when necessary.

[0152] Active hydrogen radicals are generated by passing hydrogenthrough a catalyst being heated. Active ozone is generated by passingoxygen through an ozonizer.

[0153] The substrate 401 is heated in an atmospheric pressure CVDapparatus. Ethyl orthosilicate is introduced into the apparatus bybubbling it contained in a tank with a carrier gas such as nitrogen.Oxygen is introduced into the apparatus through the ozonizer. Hydrogenis introduced into the apparatus through the catalyst. All of thosegases are supplied to the substrate 401 in a mixed state from a gasnozzle having a dispersing mechanism.

[0154] In forming a film by atmospheric pressure CVD by using only ethylorthosilicate and ozone, an oxide film is formed much differentlydepending on whether the surface of a substrate is hydrophilic orhydrophobic. While a clean film can be formed on a substrate having ahydrophobic surface, abnormal film formation or reduction in filmforming rate likely occurs with a hydrophilic surface.

[0155] The invention, which is associated with the use of hydrogenradicals, can not only provide the decarbonization effect but alsoprevent abnormal film formation and reduction in film forming ratebecause active hydrogen terminates the substrate surface to therebycreate a hydrophobic surface. In particular, these effects areremarkable when hydrogen is introduced by an amount 0.01 to 1 times theamount of the N₂ carrier gas. Where ethyl orthosilicate is directlygasified by heating it, these effects are enhanced when hydrogen isintroduced by an amount 0.1 to 1 times the amount of the ethylorthosilicate.

[0156]FIG. 5B shows a state that amorphous silicon was formed as anactive layer 403 on the undercoat film 402 that was formed on thesubstrate 401.

[0157] The amorphous silicon film was formed at a thickness of 50-3,000Å, typically 400-1,000 Å, by plasma CVD, low-pressure thermal CVD,sputtering, or the like. In this embodiment, the amorphous silicon filmwas formed by plasma CVD by decomposing silane with the substratetemperature set at 200-400° C., typically 250-350° C.

[0158] Thereafter, the amorphous silicon film was polycrystallized(i.e., converted into a polysilicon film) by causing it to undergo whatis called solid-phase growth. This is done at a temperature lower than600° C. by using the inventions described in Japanese Unexamined PatentPublication Nos. Hei. 6-232059, Hei. 6-244103, and Hei. 6-244104 of thepresent assignee. Unless hydrogen is removed from the amorphous siliconfilm to some extent before the solid-phase growth, heating for thesolid-phase growth may cause abrupt release of hydrogen from theamorphous silicon film, forming holes in the worst case. Therefore, itis effective to add, before the solid-phase growth, a hydrogen removalstep that is performed at 400-500° C. (typically 400° C.) for 0.5-5hours (typically 1-2 hours) in a nitrogen atmosphere.

[0159] The solid-phase growth is associated with what is called ashrinkage problem (contraction of the substrate 401) except for a casewhere the substrate 401 has a high strain temperature as in the case ofquartz. The shrinkage problem can be avoided to some extent byestablishing a high initial temperature in advance and performing asubsequent process at a temperature lower than the initial temperature.That is, in doing the solid-phase growth, it is also necessary to take acertain measure against the shrinkage problem.

[0160] By using the inventions described in the above-mentioned threepublications, the solid-phase growth can be effected at a temperaturelower than 600° C., for instance, 500° C. Without the use of thismethod, the solid-phase growth takes about 4-24 hours at 600° C.

[0161] The solid-phase growth converts amorphous silicon intopolysilicon in the active layer 403. Where the polysilicon active layer403 contains a small amount of amorphous components, it is effective tocrystallize the amorphous components by applying laser light to theactive layer 403.

[0162] It is also effective to convert amorphous silicon intopolysilicon in the active layer 403 by illuminating it with laser lightafter the hydrogen removal step instead of performing the solid-phasegrowth by heating. As for the laser-related conditions, examples of thelaser light source are excimer lasers of ArF, ArCl, KrF, KrCl, XeF,XeCl, etc. The laser light energy (density) is 400-1,000 mJ at the exitof the laser main body, and 150-500 mJ/cm² on the surface of thesubstrate 401 (shaped by an optical system). These energy (density)values are ones per shot of laser light. The substrate temperature isthe room temperature to 300° C. The repetition frequency of illuminationis 20-100 Hz. The movement speed of a laser beam relatively to thesubstrate 401 is 1-5 mm/sec in which a laser beam is moved to scan thesubstrate 401 or a stage mounted with the substrate 401 is moved. Inthis embodiment, a KrF excimer laser was used and the laser light energydensity was set at 550-650 mJ at the exit of the laser main body and at180-230 mJ/cm² on the substrate 401. The repetition frequency ofillumination was set at 35-45 Hz. A stage mounted with the substrate 401was moved at 2.0-3.0 mm/sec.

[0163]FIG. 5C shows a state that after amorphous silicon was convertedinto polysilicon in the active layer 403 that is formed on the substrate401 through the undercoat film 402, the active layer 403 was patternedinto an island 404. The island 404 was formed by patterning a resist byknown photolithography and then etching the active layer 403 using aresist pattern as a mask. The etching may be performed by wet etching,dry etching, etc. In this embodiment, a parallel plate high-frequencyplasma processing apparatus using CF₄ and O₂ was used.

[0164]FIG. 5D shows a state that a gate insulating film 405 was soformed as to cover the island 404. The invention is applied to theformation of the gate insulating film 405 because the interface betweenthe island 404 and the gate insulating film 405 greatly influences thecharacteristics of a TFT finally produced. In this connection, thecleaning of the island 404 before the formation of the gate insulatingfilm 405 is very important. It was well known that organic substancessuch as carbon can be eliminated by cleaning with a solution obtained byadding sulfuric acid to a hydrogen peroxide solution or dry ashing withoxygen plasma. However, a study of the present assignee revealed thatthe elimination of carbon is not that simple.

[0165] As for sources of the carbon contamination, a photoresist that isused to form a desired pattern in a photolithographic process is aphotosensitive organic substance and may cause carbon contamination.Thin film processes are now indispensable in manufacturing asemiconductor device, and a vacuum apparatus is absolutely necessary forsuch processes. Certain types of vacuum pumps for evacuating a vacuumapparatus still use oil, which likely causes carbon contamination. Otherpossible sources of the carbon contamination include vapor from asubstrate carrier made of Teflon (PFA), polypropylene (PP),polyvinylidene fluoride (PVDF), ethylene trifluoride resin (ECTFE),ethylene tetrafluoride resin (ETFE), and polyethylene (PE), and floorand wall materials used in a clean room.

[0166] A conventional method is such that dry ashing is performed beforea photolithographic step, organic substances are removed by applying,immediately before each step, a solution (heated to 80° C.) of ahydrogen peroxide solution and sulfuric acid (1:1) (hereinafter calledwet ashing), and the next processing is performed immediately.

[0167] Although the previous understanding was such that almost allorganic substances can be eliminated by the dry ashing and wet ashing,carbon contamination evaluation of substrate surfaces by a known XPStechnique has revealed that only C—C bonds are scarcely removed.

[0168] Hydrogen radicals or hydrogen ions act effectively to eliminateC—C single bonds attached to the substrate surface. Although the use ofonly hydrogen radicals is sufficient, it has been found that the effectof eliminating C—C single bonds is enhanced by adding oxygen radicals,ozone, or oxygen ions. This is considered due to a phenomenon thathydrogen and oxygen radicals etc. react with carbon bonds to form suchgases as CH_(x), CO_(x) and COH, that is, gasify carbon.

[0169] To generate hydrogen radicals or hydrogen ions, a substrate isplaced in a parallel plate plasma apparatus, for instance. In this case,it is preferable to dispose the substrate on the anode side to preventit from being damaged by plasma ions etc. It is also preferable that theapparatus be adapted to be able to heat a substrate, in which case thecarbon elimination effect is enhanced by additional removal by heat.

[0170] Plasma is generated by introducing a hydrogen gas into theapparatus and applying high-frequency power between the parallel plates.Highly active, neutral hydrogen radicals are generated in the plasma, aswell as hydrogen ions and electrons. While increasing the high-frequencypower is effective to increase the amount of hydrogen radicals and ions,it can further be increased by utilizing electron cyclotron resonancewith microwaves. Generated hydrogen radicals and ions reach thesubstrate surface, and react with C—C single bonds there to therebyeliminate carbon bonds. A resulting carbon gas is exhausted by a pump.

[0171] To clean the surface of the island 404, carbon contaminants areremoved to some extent first by immersing, for 5-10 minutes, thesubstrate structure in a mixture of sulfuric acid and hydrogen peroxidesolution (1:1; 80° C.), and then heavy metals were removed by immersing,for 5-10 minutes, the substrate structure in a mixture of hydrochloricacid and hydrogen peroxide solution (1:1; 80° C.). This type of cleaningis omitted if it adversely affects the substrate 401 etc. Then, toremove carbon contaminants containing carbon single bonds at least astheir parts from the surface of the island 404, the substrate structurewas placed in a plasma processing apparatus.

[0172] Since this plasma processing apparatus is also used to form agate insulating film 405 after cleaning the island 404, it is desirablethat the apparatus be so constructed as to allow the formation of thegate insulating film 405 and the removal of carbon contaminantscontaining carbon single bonds at least as their parts to be performedin the same reaction chamber. Examples of the apparatus which servesboth as the apparatus for forming the gate insulating film 405 and asthe plasma processing apparatus for removing carbon contaminantscontaining carbon single bonds at least as their parts are a parallelplate plasma CVD apparatus, a microwave plasma CVD apparatus utilizingelectron cyclotron resonance, and an electrodeless discharge plasma CVDapparatus in which electrodes are arranged around a quartz chamber. Inthis embodiment, a parallel plate plasma CVD apparatus was used.

[0173] To effect plasma processing for removing carbon contaminantscontaining carbon single bonds at least as their parts, the substrate401 formed with the island 404 was placed on the anode side of theparallel plate plasma processing apparatus. The interval between theanode and the cathode (parallel plate electrodes) was adjusted in arange of 30-150 mm. The typical interval was 70 mm. No serious problemsoccurred even with an interval larger or smaller than 70 mm if theconditions were selected properly. Gases were introduced into thereaction space through the cathode electrode that was so constructed asto serve as a shower head. The shower head was provided with adispersing plate or the like so that gases were uniformly applied to thesurface of the substrate 401. A hydrogen gas and an oxygen gas wereintroduced by the same amount. The gas amounts were so set that theplasma processing pressure became 50 mTorr to 10 Torr and the gasresidence time became less than 5 seconds though these values depend onthe size of the processing chamber. The residence time was set less than5 seconds to quickly exhaust removed carbon because there sometimesoccurred re-attachment of gasified carbon. However, there occurred noproblems if the residence time was less than about 10 seconds. Forexample, the residence time is about 10 seconds if a gas is introducedat 316 SCCM into a chamber of 40 liters at a pressure of 1 Torr, sincethe residence time is equal to the product of the chamber capacity andthe chamber pressure divided by the gas flow rate. Therefore, todecrease the residence time, it is necessary to reduce the chambercapacity or pressure or increasing the gas flow rate.

[0174] In this embodiment, the residence time was set at about 4 secondsby making the chamber capacity, processing pressure, and the flow ratesof oxygen and hydrogen 40 liters, 1 Torr, 400 SCCM, and 400 SCCM,respectively.

[0175] Plasma was generated by high-frequency discharge. The frequencyof the high-frequency power was set at 10-100 MHz, and at 20 MHz in thisembodiment. The application power was 0.1-2 W/cm². If the power is lowerthan 0.1 W/cm², the processing time becomes too long though carbon canbe eliminated. On the other hand, if the power is higher than 2 W/cm²,the electrodes are heated. Since it is necessary to cool the electrodes,the apparatus becomes large and expensive. In this embodiment, power of0.8 W/cm² was applied. The carbon removal ability is improved by heatingthe substrate, typically to 200-500° C. Although a sufficient carbonremoval effect is obtained in a range from the room temperature to 200°C., the substrate temperature was set at 300-400° C. which is the sameas a substrate temperature in forming the gate insulating film 405subsequently. The plasma processing time was about 1-10 minutes. Theplasma processing time varies very much with various conditions such asthe gas residence time, the frequency of high-frequency power, theapplication power, and the substrate temperature. It should not be toolong when considered part of the time of a manufacturing process. Inthis embodiment, it was set at 2 minutes.

[0176] H₂O may be used to generate hydrogen radicals etc. and oxygenradicals etc. instead of using hydrogen and oxygen gases. H₂O can beintroduced in several manners. One method is to bubble H₂O in a tankwith an inert carrier gas such as He, Ne or Ar and then transport aresulting H₂O gas to the processing chamber. Another method is totransport a H₂O gas to the processing chamber by increasing its vaporpressure by heating the entire pipe from a H₂O tank to the processingchamber. H₂O as introduced is decomposed by plasma to generate hydrogenions, hydrogen radicals, oxygen ions, oxygen radicals, and ozone at thesame time. Similar effects were obtained by bubbling H₂O in a tank witha He carrier gas that was supplied at 500-1,000 SCCM.

[0177] After the step of eliminating carbon contaminants containingcarbon single bonds at least as their parts, the gate insulating film405 was formed by using ethyl orthosilicate (also called TEOS), oxygen,and hydrogen. It is effective to use other types of organic silane suchas OMCTS (octamethylcyclotetrasiloxane) and HMDS (hexamethyldisiloxane)instead of ethyl orthosilicate. The substrate temperature was set at200-500° C., typically 300-400° C. The film forming pressure was set at0.1-2 Torr, typically 0.5-1 Torr. The frequency of the plasma powersupply was 5-50 MHz, typically 20 MHz, and its supply power was 0.1-2W/cm², typically 0.3-0.5 W/cm². The ratio of ethyl orthosilicate tooxygen was set at 1:5-20, typically 1:10. As for the amount of hydrogen,the ratio of ethyl orthosilicate to hydrogen was set at 1:0.01-1,typically 1:0.5. The gate insulating film 405 was formed at a thicknessof 250-2,000 Å, typically 500-1,200 Å.

[0178] During the film formation, carbon was removed being gasified intoCH_(x) and COH by hydrogen radicals and hydrogen ions. After completionof the above step, the carbon content in the gate insulating film 405was measured by SIMS. Whereas oxide films that were formed as the gateinsulating film 405 without adding hydrogen had a minimum carbon contentvalue in a depth-direction profile of 1×10¹⁹ cm⁻³, oxide films that wasformed as the gate insulating film 405 with the addition of hydrogen hada corresponding value of 2×10¹⁸ to 7×10¹⁸ cm⁻³.

[0179] A gate electrode film was formed on the gate insulating film 405,and then patterned into a gate electrode 406. Impurity regions for asource and a drain 407 were then formed to provide a state of FIG. 5E.More specifically, after a conductive film of Al, doped polysilicon, Cr,Ta, or the like was laid, a resist film was patterned byphotolithography. The gate electrode 406 was formed by etching theconductive film into a desired shape by using the resist pattern as amask. In this embodiment, an Al film was formed by sputtering.Thereafter, the source and drain 407 were formed by through-doping theisland 404 with phosphorus by ion implantation at a dose of 5×10¹⁵ cm⁻².Instead of using ion implantation, PH_(x) may be implanted by plasmadoping. After the implantation, the substrate structure was heated at600° C. for 5 hours to activate the implanted ions. A doped polysiliconfilm may be deposited to form the gate electrode 406 with polysiliconrather than metal. It is also possible to deposit a non-dopedpolysilicon film and then dope it by ion implantation or plasma dopingto form the source and drain 407.

[0180] Subsequently, an interlayer insulating film 408 was formed, and acontact electrode 409 for the gate electrode 406 and contact electrodes410 for the source and drain 407 were formed. Thus, a top-gatepolysilicon thin-film transistor was completed as shown in FIG. 5F. Theinvention was used in forming the interlayer insulating film 408. Informing the interlayer insulating film 408 by atmospheric pressure CVD,carbon can be eliminated during the film formation by generatinghydrogen radicals by a catalyst method and using those during the filmformation. The invention is also effective in an atmospheric pressureCVD method using organic silane. In the case of applying the inventionto film formation by atmospheric pressure CVD, a catalyst method is usedto convert hydrogen to hydrogen radicals. Proper examples of thecatalyst include 3d-transition metals such as platinum, palladium,reduced nickel, cobalt, titanium, vanadium, and tantalum; compounds ofmetals such as aluminum, nickel, platinum-silicon, platinum-chlorine,platinum-rhenium, nickel-molybdenum, and cobalt-molybdenum; and mixturesor compounds of any of the above transition metals and alumina or silicagel. In addition, Raney catalysts of cobalt, ruthenium, palladium,nickel, and the like, and mixtures or compounds of any of those Raneycatalysts and carbon can be used. These catalysts are used in agranulated, reticular, or powder state. Materials having a low meltingpoint and markedly increasing the initial absorption rate of a reactivesubstance, and materials containing alkali metals such as sodium whicheasily vaporize are not suitable for the catalyst. Examples of suchunfavorable materials are copper and tungsten. Experiments revealedconsiderable degradation of a catalyst at a temperature higher than thedecomposition temperature of a reactive substance. The amount and thedensity of a catalyst depend on the effective contact area with areactive gas, and may be adjusted when necessary. Active hydrogenradicals are generated by passing hydrogen through a catalyst beingheated. Active ozone is generated by passing oxygen through an ozonizer.

[0181] In an atmospheric CVD apparatus in which the substrate structureis heated, ethyl orthosilicate is introduced into the apparatus bybubbling it contained in a tank with a carrier gas such as nitrogen.Oxygen is introduced into the apparatus through the ozonizer. Hydrogenis introduced into the apparatus through the catalyst. All of thosegases are supplied to the substrate structure in a mixed state from agas nozzle having a dispersing mechanism. It is very effective tointroduce hydrogen by an amount 0.01 to 1 times the amount of the N₂carrier gas. Where ethyl orthosilicate is directly gasified by heatingit, the effects are enhanced when hydrogen is introduced by an amount0.1 to 1 times the amount of the ethyl orthosilicate. In thisembodiment, hydrogen radicals were generated from hydrogen by using Niwith a catalyst temperature of 500° C. The amount of hydrogen was set at0.3-0.8 times the amount of the N₂ carrier gas. The substratetemperature was set at 350° C. Thus, the interlayer insulating film 408was formed at a thickness of 7,000-15,000 Å, typically 9,000-12,000 Å.

[0182] Although in this embodiment all of the undercoat film 402, thegate insulating film 405, and the interlayer insulating film 408 areoxide films formed by using organic silane, only one those films may bean oxide film formed according to the embodiment. That is, since in theembodiment an oxide film is formed by removing carbon during the filmformation that uses an organic silane type gas, the embodiment need notbe used in film formation in which organic silane is not used. Further,where a film property other than a small carbon content is important,the use of an oxide film of the invention may be avoided. For example,only the undercoat film 402 and the interlayer insulating film 408 maybe oxide films formed according to the invention, while the gateinsulating film 405 is a thermal oxidation film or an oxide film formedby using silane and oxygen. Other various combinations of oxide filmsare also possible.

[0183] TFTs completed by using oxide films of the embodiment had achannel length of 8 μm and a channel width of 100 μm. As for thecharacteristics, the mobility was 153 cm²/Vs in the case of N-channelTFTs and 119 cm²/Vs in the case of P-channel TFTs, and the kink effectwas not observed at all. No variation occurred in moisture resistanceafter TFTs were left in an atmosphere of 150° C. and 60% RH for 12hours. The moisture resistance should have been further improved if TFTshad a SiNe protection film as in an ordinary case. Thus, TFTs wereimproved in characteristics and reliability because the carbon contentwas greatly reduced in all of the undercoat film 402, the gateinsulating film 405, and the interlayer insulating film 408 as comparedto the case where oxide films of the embodiment were not used.

[0184] Embodiment 6

[0185] This embodiment is directed to a case of forming nitrogen-addedoxide films as an undercoat film 402, a gate insulating film 405, aninterlayer insulating film 408 in the thin-film transistor manufacturingprocess using polysilicon shown in FIGS. 5A-5F. A manufacturing processof this embodiment will be described with reference to FIGS. 5A-5F, butthe same steps as in the fifth embodiment will not be described.

[0186] An undercoat film 402 was formed by using a parallel plate plasmaCVD apparatus and gases of ethyl orthosilicate (also called TEOS), NO,and hydrogen. It is effective to use other types of organic silane suchas OMCTS (octamethylcyclotetrasiloxane) and HMDS (hexamethyldisiloxane)instead of ethyl orthosilicate. The substrate temperature was set at200-500° C., typically 400° C. The film forming pressure was set at0.1-2 Torr, typically 1 Torr. The frequency of the plasma power supplywas 5-50 MHz, typically 20 MHz, and its supply power was 0.1-2 W/cm²,typically 0.3 W/cm². The ratio of ethyl orthosilicate to NO was set at1:5-20, typically 1:5. As for the amount of hydrogen, the ratio of ethylorthosilicate to hydrogen was set at 1:0.01-1, typically 1:0.5. Theundercoat film 402 was formed at a thickness of 500-3,000 Å, typically2,000 Å.

[0187] It is very effective to remove carbon during the formation of theundercoat film 402 by hydrogen radicals and hydrogen ions in any plasmaCVD method even other than the parallel plate plasma CVD, if an oxidefilm is formed by using organic silane.

[0188] In forming the undercoat film 402 by atmospheric pressure CVD,carbon can also be eliminated during the film formation by generatinghydrogen radicals by a catalyst method and using those during the filmformation. The invention is also effective in an atmospheric pressureCVD method using organic silane.

[0189] The kink effect is prevented or reduced in possibility ofoccurrence by using the invention in forming the undercoat film 402. Thepossibility of occurrence of the kink effect is small if the undercoatfilm 402 is a SiO_(x) film that does not contain impurities. It isnecessary to block diffusion of impurities from the substrate 401.

[0190] In an atmospheric CVD apparatus in which the substrate structureis heated, ethyl orthosilicate is introduced into the apparatus bybubbling it contained in a tank with a carrier gas such as nitrogenoxide. Oxygen is introduced into the apparatus through an ozonizer.Hydrogen is introduced into the apparatus through a catalyst. All ofthose gases are supplied to the substrate structure in a mixed statefrom a gas nozzle having a dispersing mechanism.

[0191] In forming a film by atmospheric pressure CVD by using only ethylorthosilicate and ozone, an oxide film is formed much differentlydepending on whether the surface of a substrate is hydrophilic orhydrophobic. While a clean film can be formed on a substrate having ahydrophobic surface, abnormal film formation or reduction in filmforming rate likely occurs with a hydrophilic surface.

[0192] The invention, which is associated with the use of hydrogenradicals, can not only provide the decarbonization effect but alsoprevent abnormal film formation and reduction in film forming ratebecause active hydrogen terminates the substrate surface to therebycreate a hydrophobic surface. In particular, these effects areremarkable when hydrogen is introduced by an amount 0.01 to 1 times theamount of nitrogen oxide. Where ethyl orthosilicate is directly gasifiedby heating it, these effects are enhanced when hydrogen is introduced byan amount 0.1 to 1 times the amount of the ethyl orthosilicate.

[0193]FIG. 5D shows a state that a gate insulating film 405 was soformed as to cover an island 404. The invention is applied to theformation of the gate insulating film 405 itself because the interfacebetween the island 404 and the gate insulating film 405 greatlyinfluences the characteristics of a TFT finally produced. In thisconnection, the cleaning of the island 404 before the formation of thegate insulating film 405 is very important. It was well known thatorganic substances such as carbon can be eliminated by cleaning with asolution obtained by adding sulfuric acid to a hydrogen peroxidesolution or dry ashing with oxygen plasma. However, a study of thepresent assignee revealed that the elimination of carbon is not thatsimple.

[0194] After a step of eliminating carbon contaminants containing carbonsingle bonds at least as their parts, the gate insulating film 405 wasformed by using ethyl orthosilicate (also called TEOS) as the organicsilane type source gas and N₂O as nitrogen oxide. It is effective to useother types of organic silane such as OMCTS(octamethylcyclotetrasiloxane) and HMDS (hexamethyldisiloxane) insteadof ethyl orthosilicate. The substrate temperature was set at 200-500°C., typically 300-400° C. The film forming pressure was set at 0.1-2Torr, typically 0.5-1 Torr. The frequency of the plasma power supply was5-50 MHz, typically 20 MHz, and its supply power was 0.1-2 W/cm²,typically 0.3-0.5 W/cm².

[0195] The ratio of ethyl orthosilicate to N₂O was set at 1:5-20,typically 1:10. As for the amount of hydrogen, the ratio of ethylorthosilicate to hydrogen was set at 1:0.01-1, typically 1:0.5. The gateinsulating film 405 was formed at a thickness of 250-2,000 Å, typically500-1,200 Å. During the film formation, carbon was exhausted from thechamber being gasified into CH_(x) and COH by hydrogen radicals andhydrogen ions.

[0196] After completion of the above step, the carbon content in thegate insulating film 405 was measured by SIMS. Whereas oxide films thatwere formed as the gate insulating film 405 without adding hydrogen hada minimum carbon content value in a depth-direction profile of 1×10¹⁹cm⁻³, oxide films that was formed as the gate insulating film 405 withthe addition of hydrogen had a corresponding value of 2×10¹⁸ to 7×10¹⁸cm⁻³.

[0197] In forming an interlayer insulating film 408, carbon can beeliminated during the film formation by generating hydrogen radicals bya catalyst method and using those during the film formation. Theinvention is also effective in an atmospheric pressure CVD method usingorganic silane.

[0198] In the case of applying the invention to film formation byatmospheric pressure CVD, a catalyst method is used to convert hydrogento hydrogen radicals. Active hydrogen radicals are generated by passinghydrogen through a catalyst being heated. Active ozone is generated bypassing oxygen through an ozonizer.

[0199] In an atmospheric CVD apparatus in which the substrate structureis heated, ethyl orthosilicate is introduced into the apparatus bybubbling it contained in a tank with nitrogen oxide such as N₂O. Oxygenis introduced into the apparatus through the ozonizer. Hydrogen isintroduced into the apparatus through the catalyst. All of those gasesare supplied to the substrate structure in a mixed state from a gasnozzle having a dispersing mechanism. It is very effective to introducehydrogen by an amount 0.01 to 1 times the amount of nitrogen oxide.Where ethyl orthosilicate is directly gasified by heating it, theeffects are enhanced when hydrogen is introduced by an amount 0.1 to 1times the amount of the ethyl orthosilicate. In this embodiment,hydrogen radicals were generated from hydrogen by using Ni with acatalyst temperature of 500° C. The amount of hydrogen was set at0.3-0.8 times the amount of nitrogen oxide. The substrate temperaturewas set at 350° C. Thus, the interlayer insulating film 408 was formedat a thickness of 7,000-15,000 Å, typically 9,000-12,000 Å.

[0200] Although in this embodiment all of the undercoat film 402, thegate insulating film 405, and the interlayer insulating film 408 areoxide films formed by using organic silane with the addition ofnitrogen, only one of those films may be an oxide film formed accordingto the embodiment. That is, since in the embodiment an oxide film isformed by removing carbon during the film formation that uses an organicsilane type gas and has an alkali metal blocking effect, the embodimentneed not be used in film formation in which organic silane is not used.Further, where a film property other than a small carbon content isimportant, the use of an oxide film of the invention may be avoided. Forexample, only the undercoat film 402 and the interlayer insulating film408 may be oxide films formed according to the invention, while the gateinsulating film 405 is a thermal oxidation film or an oxide film formedby using silane and oxygen. Other various combinations of oxide filmsare also possible.

[0201] TFTs completed by using the embodiment had a channel length of 8μm and a channel width of 100 μm. As for the characteristics, themobility was 153 cm²/Vs in the case of N-channel TFTs and 119 cm²/Vs inthe case of P-channel TFTs, and the kink effect was not observed at all.No variation occurred in moisture resistance after TFTs were left in anatmosphere of 150° C. and 60% RH for 12 hours. The moisture resistanceshould have been further improved if TFTs had a SiN_(x) protection filmas in an ordinary case. Thus, TFTs were improved in characteristics andreliability because the carbon content was greatly reduced and animproved blocking effect with respect to impurities such as alkalimetals was obtained in all of the undercoat film 402, the gateinsulating film 405, and the interlayer insulating film 408 as comparedto the case where oxide films of the embodiment were not used.

[0202] Embodiment 7

[0203] This embodiment is directed to a case in which the invention isapplied to formation of an insulating film for burying and planarizingline-and-space wiring lines that are arranged side by side.

[0204]FIG. 6 shows how metal wiring lines are buried.

[0205] A thermal oxidation film 52 is formed on a semiconductorsubstrate 51, metal wiring lines 53 are formed thereon, and a buryinginsulating film 54 is further formed thereon. Although a single crystalsilicon wafer is mainly used as the semiconductor substrate 51, it maybe a compound semiconductor substrate such as a GaAs substrate or apolycrystalline semiconductor substrate. In this embodiment, a P-typesilicon wafer of the (100) plane is used. The thermal oxidation film 52may be either a film formed by wet oxidation or a film formed by dryoxidation. In this embodiment, the thermal oxidation film 52 was grownby dry oxidation at a thickness of about 500 Å over the entire surfaceof the semiconductor substrate 51. To form the metal wiring lines 53thereon, an Al film was deposited by sputtering. The Al sputtering wasperformed by using a target containing Si at 2% to prevent Al hillocks.The Al film was shaped by anisotropic dry etching into the metal wiringlines 53 of 1 μm both in thickness and height (aspect ratio: 1). Thewiring line interval was varied in a range of 0.3-1.0 μm.

[0206] The invention was used in forming the insulating film 54. Whilefilm forming methods according to the invention using organic silaneinclude a plasma CVD method and an atmospheric pressure CVD method, inthis embodiment the insulating film 54 was formed by the atmosphericpressure CVD method. In forming the insulating film 54 by atmosphericpressure CVD, carbon can be eliminated during the film formation bygenerating hydrogen radicals by a catalyst method and using those duringthe film formation. The invention is also effective in an atmosphericpressure CVD method using organic silane. In the case of applying theinvention to film formation by atmospheric pressure CVD, a catalystmethod is used to convert hydrogen to hydrogen radicals. Proper examplesof the catalyst include 3d-transition metals such as platinum,palladium, reduced nickel, cobalt, titanium, vanadium, and tantalum;compounds of metals such as aluminum, nickel, platinum-silicon,platinum-chlorine, platinum-rhenium, nickel-molybdenum, andcobalt-molybdenum; and mixtures or compounds of any of the abovetransition metals and alumina or silica gel. In addition, Raneycatalysts of cobalt, ruthenium, palladium, nickel, and the like, andmixtures or compounds of any of those Raney catalysts and carbon can beused. These catalysts are used in a granulated, reticular, or powderstate. Materials having a low melting point and markedly increasing theinitial absorption rate of a reactive substance, and materialscontaining alkali metals such as sodium which easily vaporize are notsuitable for the catalyst. Examples of such unfavorable materials arecopper and tungsten. Experiments revealed considerable degradation of acatalyst at a temperature higher than the decomposition temperature of areactive substance. The amount and the density of a catalyst depend onthe effective contact area with a reactive gas, and may be adjusted whennecessary. Active hydrogen radicals are generated by passing hydrogenthrough a catalyst being heated. Active ozone is generated by passingoxygen through an ozonizer. In an atmospheric CVD apparatus in which thesubstrate structure is heated, ethyl orthosilicate is introduced intothe apparatus by bubbling it contained in a tank with a carrier gas suchas nitrogen. Oxygen is introduced into the apparatus through theozonizer. Hydrogen is introduced into the apparatus through thecatalyst. All of those gases are supplied to the substrate structure ina mixed state from a gas nozzle having a dispersing mechanism.

[0207] In forming a film by atmospheric pressure CVD by using only ethylorthosilicate as organic silane and ozone, an oxide film is formed muchdifferently depending on whether the surface of a substrate ishydrophilic or hydrophobic. While a clean film can be formed on asubstrate having a hydrophobic surface, abnormal film formation orreduction in film forming rate likely occurs with a hydrophilic surface.In the case of forming the insulating film 54, it can be formed on themetal wiring lines 53 without causing any problems. However, since thesurface of the thermal oxidation film 52 is hydrophilic, abnormal filmformation likely occurs conventionally unless low-density ozone is usedat the. initial stage of film formation and then high-density ozone isused. That is, conventionally, there are problems when a film is formedon at least part of a hydrophilic surface. In contrast, the invention,which is associated with the use of hydrogen radicals, can not onlyprovide the decarbonization effect but also prevent abnormal filmformation and reduction in film forming rate because active hydrogenterminates the substrate surface to thereby create a hydrophobicsurface. Therefore, in the invention, film formation can be performedwithout changing the ozone density from the initial stage to the end ofthe film formation, to provide a thickness-direction profile having onlya small variation. In this embodiment, the film formation was performedwith the ozone density set at 1.5-3%

[0208] A F-doped SiO_(x) film having a low carbon content and a smallerpermittivity than non-doped SiO_(x) can be formed by using organicsilane containing fluorine such as FSi(OC₂H₆)₄ instead of ethylorthosilicate. Therefore, it is possible to reduce a lateral capacitancebetween wiring lines of an LSI. These effects are remarkable whenhydrogen is introduced by an amount 0.01 to 1 times the amount of the N₂carrier gas. Where ethyl orthosilicate is directly gasified by heatingit, these effects are enhanced when hydrogen is introduced by an amount0.1 to 1 times the amount of the ethyl orthosilicate.

[0209] In completed structures of this embodiment, the metal wiringlines 53 were buried completely by the insulating film 54 when thewiring line interval was 0.5-1.0 μm. According to the conventionalmethods without addition of hydrogen, the burying was complete whenlow-density ozone (less than 1%) was used at the initial stage of filmformation and then the ozone density was increased. However, whenhigh-density ozone (more than 1%) was used from the initial stage offilm formation, abnormal film formation occurred on the thermaloxidation film 52 and burying could not be effected. Where the wiringline interval was 0.3-0.5 μm, burying could not be effected completely(the performance became worse as the interval became closer to 0.3 μm)irrespective of the use of the invention. This would indicate the limitof the atmospheric pressure CVD as a film forming method.

[0210] The hygroscopicity of completed films were evaluated after theywere left in an atmosphere of 60° C. and 80% RH for 50 hours. Noinfrared absorption mode due to moisture absorption was detected infilms formed according to the invention. In contrast, a Si—OH infraredabsorption mode was detected in the vicinity of 3,660 cm⁻¹ in all filmsthat were formed without using the invention.

[0211] Embodiment 8

[0212] This embodiment is directed to a case in which the invention isapplied to formation of an insulating film for burying and planarizingline-and-space wiring lines that are arranged side by side. In thisembodiment, an insulating film 54 is an oxide film formed by addingnitrogen.

[0213]FIG. 6 shows how metal wiring lines are buried. As in the case ofthe seventh embodiment, a thermal oxidation film 52 of about 500 Å inthickness is formed on a semiconductor substrate 51, and metal wiringlines 53 are formed thereon. The metal wiring lines 53 were formed bypatterning an Al film by anisotropic dry etching into wiring lines of 1μm both in thickness and height (aspect ratio: 1). The wiring lineinterval was varied in a range of 0.3-1.0 μm.

[0214] The invention was used in forming the insulating film 54. Whilefilm forming methods according to the invention using organic silaneinclude a plasma CVD method and an atmospheric pressure CVD method, inthis embodiment the insulating film 54 was formed by the atmosphericpressure CVD method. In forming the insulating film 54 by atmosphericpressure CVD, carbon can be eliminated during the film formation bygenerating hydrogen radicals by a catalyst method and using those duringthe film formation. The invention is also effective in an atmosphericpressure CVD method using organic silane.

[0215] In the case of applying the invention to film formation byatmospheric pressure CVD, a catalyst method is used to convert hydrogento hydrogen radicals as in the case of the seventh embodiment.

[0216] Active hydrogen radicals are generated by passing hydrogenthrough a catalyst being heated. Active ozone is generated by passingoxygen through an ozonizer. In an atmospheric CVD apparatus in which thesubstrate structure is heated, HMDS contained in a tank is bubbled withN₂O. Oxygen is introduced into the apparatus through the ozonizer.Hydrogen is introduced into the apparatus through the catalyst. All ofthose gases are supplied to the substrate structure in a mixed statefrom a gas nozzle having a dispersing mechanism.

[0217] In forming a film by atmospheric pressure CVD by using only HMDSas organic silane and ozone, an oxide film is formed much differentlydepending on whether the surface of a substrate is hydrophilic orhydrophobic. While a clean film can be formed on a substrate having ahydrophobic surface, abnormal film formation or reduction in filmforming rate likely occurs with a hydrophilic surface.

[0218] In the case of forming the insulating film 54, it can be formedon the metal wiring lines 53 without causing any problems. However,since the surface of the thermal oxidation film 52 is hydrophilic,abnormal film formation likely occurs conventionally unless low-densityozone is used at the initial stage of film formation and thenhigh-density ozone is used. That is, conventionally, there are problemswhen a film is form ed on at least part of a hydrophilic surface. Incontrast, the invention, which is associated with the use of hydrogenradicals, can not only provide the decarbonization effect but alsoprevent abnormal film formation and reduction in film forming ratebecause active hydrogen terminates the substrate surface to therebycreate a hydrophobic surface. Therefore, in the invention, filmformation can be performed without changing the ozone density from theinitial stage to the end of the film formation, to provide athickness-direction profile having only a small variation. In thisembodiment, the film formation was performed with the ozone density setat 1.5-3%

[0219] A F-doped SiO_(x) film having a low carbon content and a smallerpermittivity than non-doped SiO_(x) can be formed by using organicsilane containing fluorine such as FSi(OC₂H₆)₄ instead of ethylorthosilicate. Therefore, it is possible to reduce a lateral capacitancebetween wiring lines of an LSI. These effects are remarkable whenhydrogen is introduced by an amount 0.01 to 1 times the amount ofnitrogen oxide. Where organic silane such as HMDS is directly gasifiedby heating it, these effects are enhanced when hydrogen is introduced byan amount 0.1 to 1 times the amount of the ethyl orthosilicate. However,in this case, care should be taken not to excessively increase theamount of nitrogen oxide such as N₂O to avoid an increase inpermittivity.

[0220] In completed structures of this embodiment, the metal wiringlines 53 were buried completely by the insulating film 54 when thewiring line interval was 0.5-1.0 μm. According to the conventionalmethods without addition of hydrogen, the burying was complete whenlow-density ozone (less than 1%) was used at the initial stage of filmformation and then the ozone density was increased. However, whenhigh-density ozone (more than 1%) was used from the initial stage offilm formation, abnormal film formation occurred on the thermaloxidation film 52 and burying could not be effected. Where the wiringline interval was 0.3-0.5 μm, burying could not be effected completely(the performance became worse as the interval became closer to 0.3 μm)irrespective of the use of the invention. This would indicate the limitof the atmospheric pressure CVD as a film forming method.

[0221] The hygroscopicity of completed films were evaluated after theywere left in an atmosphere of 60° C. and 80% RH for 50 hours. Noinfrared absorption mode due to moisture absorption was detected infilms formed according to the invention. In contrast, a Si—OH infraredabsorption mode was detected in the vicinity of 3,660 cm⁻¹ in all filmsthat were formed without using the invention.

[0222] The invention provides a semiconductor device manufacturingmethod which enables formation of a film that is superior in stepcoverage, lower in carbon content than conventional films, and low inhygroscopicity, thereby improving the characteristics and thereliability of a semiconductor device. The invention also provides asemiconductor device manufacturing apparatus to implement the abovemanufacturing method. By using this apparatus, it becomes possible toeliminate carbon during film formation using an organic silane typesource gas.

[0223] Further, by using an oxide film formed according to theinvention, there can be obtained superior step coverage, a lower carboncontent than in conventional films, low hygroscopicity, superiorperformance of blocking impurities such as alkali metals, and othersuperior characteristics, whereby the characteristics and thereliability of a semiconductor device can be improved.

[0224] The invention also provides a semiconductor device manufacturingapparatus to implement the above manufacturing method for improving thecharacteristics and the reliability of a semiconductor device. By usingthis apparatus, it becomes possible to eliminate carbon during filmformation using an organic silane type source gas.

What is claimed is:
 1. A method of manufacturing a semiconductor devicecomprising: placing a substrate in a reaction chamber; passing H₂through a heated catalyst to form a hydrogen radical; introducing anorganic silane type source gas and a nitrogen oxide and said hydrogenradical into said reaction chamber at a flow rate ratio of organicsilane type source gas:nitrogen oxide:hydrogen radical=1:1-15:0.01-1 interms of SCCM; and forming an oxide film over said substrate by CVD byusing said organic silane type source gas and said nitrogen oxide andsaid hydrogen radical.
 2. A method of manufacturing a semiconductordevice comprising: placing a substrate in a reaction chamber; passing H₂through a heated catalyst to form a hydrogen radical; introducing anorganic silane type source gas and a nitrogen oxide and said hydrogenradical into said reaction chamber; and forming an oxide film over saidsubstrate by CVD by using said organic silane type source gas and saidnitrogen oxide and said hydrogen radical.
 3. A method of manufacturing asemiconductor device comprising: placing a substrate in a reactionchamber; passing H₂ through a heated catalyst to form a hydrogenradical; introducing a source gas comprising silicon and a nitrogenoxide and said hydrogen radical into said reaction chamber; and formingan oxide film over said substrate by CVD by using said source gascomprising silicon and said nitrogen oxide and said hydrogen radical. 4.A method of manufacturing a semiconductor device comprising: placing asubstrate in a reaction chamber; passing H₂ through a heated catalyst toform a hydrogen radical; introducing a source gas comprising silicon anda nitrogen oxide and said hydrogen radical into said reaction chamber;forming an undercoat oxide film over said substrate by CVD by using saidsource gas comprising silicon and said nitrogen oxide and said hydrogenradical; and forming a semiconductor layer to become an active layer ofa thin film transistor over said undercoat oxide film.
 5. A method ofmanufacturing a semiconductor device comprising: forming a semiconductorlayer to become an active layer of a thin film transistor over asubstrate; placing said semiconductor layer formed over said substratein a reaction chamber; passing H₂ through a heated catalyst to form ahydrogen radical; introducing a source gas comprising silicon and anitrogen oxide and said hydrogen radical into said reaction chamber; andforming an oxide film as an interlayer insulating film over saidsemiconductor layer by CVD by using said source gas comprising siliconand said nitrogen oxide and said hydrogen radical.
 6. A method accordingto claim 1 wherein said nitrogen oxide is selected from the groupconsisting of N₂O, NO, N₂O₃, NO₂, N₂O₄, N₂O₅, NO₃, N₂O₆.
 7. A methodaccording to claim 1 wherein said organic silane type source gas isselected from the group consisting of ethyl orthosilicate,octamethylcyclotetrasiloxane and hexamethyldisiloxane.
 8. A methodaccording to claim 1 wherein said organic silane type source gas is amaterial including fluorine.
 9. A method according to claim 1 whereinsaid substrate is heated.
 10. A method according to claim 2 wherein saidnitrogen oxide is selected from the group consisting of N₂O, NO, N₂O₃,NO₂, N₂O₄, N₂O₅, NO₃, N₂O₆.
 11. A method according to claim 2 whereinsaid organic silane type source gas is selected from the groupconsisting of ethyl orthosilicate, octamethylcyclotetrasiloxane andhexamethyldisiloxane.
 12. A method according to claim 2 wherein saidorganic silane type source gas is a material including fluorine.
 13. Amethod according to claim 2 wherein said substrate is heated.
 14. Amethod according to claim 3 wherein said nitrogen oxide is selected fromthe group consisting of N₂O, NO, N₂O₃, NO₂, N₂O₄, N₂O₅, NO₃, N₂O₆.
 15. Amethod according to claim 3 wherein said substrate is heated.
 16. Amethod according to claim 4 wherein said nitrogen oxide is selected fromthe group consisting of N₂O, NO, N₂O₃, NO₂, N₂O₄, N₂O₅, NO₃, N₂O₆.
 17. Amethod according to claim 4 wherein said substrate is heated.
 18. Amethod according to claim 5 wherein said nitrogen oxide is selected fromthe group consisting of N₂O, NO, N₂O₃, NO₂, N₂O₄, N₂O₅, NO₃, N₂O₆.
 19. Amethod according to claim 5 wherein said substrate is heated.